A conventional in-wheel motor drive unit 101 is disclosed in Japanese Unexamined Patent Publication No. 2006-258289, for example. Referring to FIG. 8, the in-wheel motor drive unit 101 includes a motor portion 103 to generate driving force in a casing 102 mounted on a vehicle body, a wheel hub bearing portion 104 directly connected to a wheel, and a speed reduction portion 105 to reduce rotation speed of the motor portion 103 and transmit it to the wheel hub bearing portion 104.
The above in-wheel motor drive unit 101 employs a low-torque high-rotation motor in the motor portion 103 to implement a compact unit. Meanwhile, high torque is required in the wheel hub bearing portion 104 to drive the wheel. Thus, the speed reduction portion 105 sometimes employs a cycloidal reducer which is compact and high in reduction ratio.
In addition, the speed reduction portion 105 using a conventional cycloidal reducer includes a motor side rotation member 106 having eccentric portions 106a and 106b, curve plates 107a and 107b arranged at the eccentric portions 106a and 106b, rolling bearings 111 rotatably supporting the curve plates 107a and 107b with respect to the motor side rotation member 106, a plurality of outer pins 108 engaging with circumference surfaces of the curve plates 107a and 107b to generate rotation movements of the curve plates 107a and 107b, and a plurality of inner pins 109 to transmit the rotation movements of the curve plates 107a and 107b to a wheel side rotation member 110.
In order to incorporate the outer pins 108 into the casing 102 in the above speed reduction portion 105, it is necessary to axially split the casing 102 into two parts at the position of the outer pin 108 and form a recession portion to hold the outer pin 108 in each of the two split casing.
At this time, unless the positions of the corresponding recession portions strictly coincide with each other, the outer pin 108 is inclined with respect to the motor side rotation member 106. When the outer pin 108 is incorporated in the inclined condition, an edge load is generated between the curve plates 107a and 107b, and the outer pin 108 and the durability of the speed reduction portion 105 is lowered.